Plastic is a material typically formed of long chain organic polymers. Because of the relatively low cost of production and ease of manufacture, plastic materials are used in a wide variety of products around the world, including many disposable products such as packaging. As consumption of disposable products formed of plastic materials increases, the associated waste plastic material also increases, leading to environmental concerns due to the long life of the plastic materials. Other issues associated with the dumping of waste plastic include soil contamination and infertility. An alternative to landfill disposal of plastic is incineration. However, this has posed problems such as damage to the furnace and the emission of harmful gases and an offensive odor. Society's ever-increasing environmental consciousness has deemed incineration a largely unpopular and unsustainable method of disposing of waste plastic.
Plastic recycling is the process of recovering scrap or waste plastic and reprocessing the material into useful products. However, unlike metal recycling, the recycling of plastic materials is challenging due to low economic returns. Recycling of plastic further faces difficulties because of the chemical nature of the long chain organic polymers. Furthermore, waste plastic materials often need sorting into the various plastic resin types, e.g. polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), for separate recycling treatments.
As plastics are formed of long chain organic polymers containing hydrogen and carbon, processes have been developed for the conversion of the long chain polymer into shorter length hydrocarbon fuel products such as petrol or diesel. These processes typically involve pyrolysis of the plastic material to reduce the long-chain polymers to polymers of smaller chain length. Current techniques for processing plastic materials into hydrocarbon fuel products often result in the production of wax and tar type products that can foul equipment and piping used in the process. In addition, the presence of particulate materials introduced to the system or formed during the reaction result in the formation of a low purity, difficult to handle sludge-like products when condensed. Furthermore, hydrocarbons condensed directly after the pyrolysis reaction are generally required to be re-heated to separate out the desired hydrocarbons.
In view of these circumstances, various attempts have recently been made to reuse plastic waste as resources. Pyrolysis is a thermochemical decomposition of organic material, such as plastic, at elevated temperature in the absence of oxygen. It involves the simultaneous change of chemical composition and physical phase and is irreversible. Pyrolysis typically occurs at temperatures in the range of 400° C.-900° C., at small excess pressure. This process, for example, is widely used in petroleum refinery for obtaining low molecular monomers from naphtha, and it can be used for waste plastic processing with fuels production as an alternative of its incineration or landfilling.
In this process, the long polymer molecules of plastic materials are broken down into shorter chains of hydrocarbons with the help of heat and pressure. Essentially, the process mimics nature in which organic materials are broken down into oil over thousands or even millions of years. The pyrolysis process achieves this with intense heat in a closed, anaerobic system over a short period. A catalyst can be used to lower the temperature and increase the yield. Other substances which can be pyrolyzed are biomass, waste tires, lubricating oils, coal and petroleum residues; waste tire pyrolysis being the most popular and the most profitable of them all. However, this process requires huge investment, incurs abundant waste of energy and waste products, and selected type of plastics are separately processed.
Therefore, there exists a need for an efficient, eco-friendly and cost-effective method for producing fuels such as solid fuel and liquid fuel from a waste material such as rubber or plastic waste.